الفهرس 
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Abstract
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Sequence Stratigraphy and Depositional History of the Upper
Cretaceous Sediments at Gabal Nezzazat and Gabal Ekma,
Southwestern Sinai,
Egypt
SUMMARY AND CONCOLUSIONS
The present study concerned with the Upper Cretaceous sediments, south-west Sinai
along the belt extending between G. Nezzazat and G. Ekma. The main objective of this study
is to conclude the depositional history and the sequence stratigraphic analysis of the Upper
Cretaceous sediments in the study area, depending upon the successive depositional events
influencing the Upper Cretaceous Sea. To achieve the goals of the study, two representative
lithologic sections were studied in details including; Gabal Nezzazat Section and Gabal Ekma
Section. Detailed field studies and laboratory analyses were applied and the following
conclusions were achieved:-
1.1. Lithostratigraphy:
Lithologically, the Upper Cretaceous sediments in the study area is divided into five
rock units; namely from older: Raha Formation, Abu Qada Formation, Wata Formation,
Matulla Formation and Sur Chalk ranging in age from Cenomanian to Maastrichtian.
1.1.1. The Raha Formation (Cenomanian):
Raha Formation is the lowermost rock unit in the examined succession. It is
unconformably overlies the Lower Cretaceous Malha Formation and conformably overlain by
Abu Qada Formation. The Raha Formation attains 55.0 m thick at G. Nezzazat and 63.0 m
thick at G. Ekma. Lithologically, it was subdivided into lower units; the lower is Abu Had
Member and the upper is Mellaha Sand Member. Generally, Abu Had Member consists of
shales interbeded with argillaceous limestone and sandstones, whereas Mellaha Sand Member
is entirely composed of sandstones. Most of the shales are fossiliferous with Cenomanian
macro-fossils such as Exogyra (Costagyrai) olisiponensis, Ceratostreon flabellatum,
Ceratostreon, Ceratostreon conicata, Ceratostreon involuta, Ilymatogyra africana,
Ilymatogyra aegyptiaca and microfossils such as Thomasenella aegyptia, Thomasenella
punica, Thomasenella fragmentaria, Cribrostomoides sinaica, Cribrostomoides paralens,
Nezzazata simplex, Ismailia neumannae, Sinainella aegyptica and ostracods such as
Veeniacythereis jezzineensis, Veeniacythereis maghrebensis, Cytherella aegyptiensis,
Cytherella gigantosulcata, Bairdia Cenomanica, Bairdia pseudosetentrionalis, Paracypris
autocaudata.
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1.1.2. Abu Qada Formation (Upper Cenomanian-Lower Turonian):
Abu Qada Formation overlies the Raha Formation and is overlain by the Wata
Formation. It attains a thickness of 43.0 m at G. Nezzazat and 40.0 m at G. Ekma. It consists
of calcareous shales limestones. Most of these shales and limestones are fossiliferous
including Exogyra (Costagyrai) overwegi, the ammonites Metioceras sp, Vascoceras sp,
Choffaticeras (Leoniceras) segne and Thomasites mesli, and microfossils Thomasenella
aegyptia , Thomasenella punica, Thomasenella fragmentaria, Ismailia neumannae and
ostracods Veeniacythereis jezzineensis, Bairdia pseudosetentrionalis and Bairdia
Cenomanica. Based upon the above faunal assemblage, Abu Qada Formation is assigned
Upper Cenomanian to Lower Turonian age.
1.1.3. Wata Formation (Middle-Upper Turonian):
The Wata Formation is generally composed of a thick succession of alternating
limestones and shales, however the limestones are more frequent in the upper half of the
formation. The Wata Formation attains 44.0 m thick at G. Nezzazat and 31.0 m thick at G.
Ekma. The Wata Formation overlies the Abu Qada Formation and underlies the Matulla
Formation. The formation is generally poor in macrofossils. It is here dated as Middle-Late-
Turonian.
1.1.4. Matulla Formation (Coniacian-Santonian):
The Matulla Formation conformably overlies the limestones of the Middle-Upper
Turonian Wata Formation and unconformably underlies the chalk and chalky limestone of the
Campanian-Maastrichtian Sudr Chalk. Matulla Formation attains 155.0 m thick at G.
Nezzazat and 80.0 m thick at G. Ekma. The formation is mainly composed of thick
sandstones, shales and limestones intercalations. It can be lithologically subdivided into two
lithologic units: a lower siliciclastic dominated unit, consists of sandstone/shale intercalations
with subordinate limestone thin interbeds and an upper carbonate-dominated unit, composed
of frequent limestone beds with a few shale interbeds.
1.1.5. Sudr Chalk (Campanian-Maastrichtian):
The Sudr Chalk unconformably overlies the Matulla Formation and unconformably
underlies the Paleocene Esna shale. The Sudr Chalk attains 90.0 m thick at G. Nezzazat and
28.0 m thick at G. Ekma. The Sudr Chalk in the study area is composed of a homogeneous
succession of snow white, massive chalk and chalky limestone interbeded with a few chert
bands. The limestones are dominantly poor in megafossils except Pycnodonte (Phygraea)
vesiculare.
1.2. Textural characteristics:
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The detailed textural analyses made herein including, bulk textural composition and
grain size analysis have provided the detailed composition of the examined formations. The
following is the concluding remarks concerning these textural characteristics:
1.2.1 The Raha Formation:-
a- Carbonate-Sand-Mud % composition:
Fifty-four (54) samples representing the Raha Formation were analyzed for their
carbonate-sand-mud % composition. Accordingly, the majority of the sediments examined
include lesser content of carbonates, however about 10% of the samples are muddy
limestones. On the other hand, the Raha Formation at G. Nezzazat is more muddy and has
uniform lithological distribution, whereas at G. Ekma the formation is more sandy and display
scattered lithological distribution from sand to mud, reflecting variable sources and different
depositional regimes. Generally, about 44.0 % of the Raha Formation is calcareous mud to
calcareous sandy mud. Sandstones, mudstones and sandy mudstones constitute minor
proportions, forming about 13.0 %, 6.0% and 9.0 % respectively. Muddy sands and
calcareous muddy sands constitute about 18.0 % of the Raha Formation sediments, mainly
encountered at G. Ekma.
b- Sand-Clay-Silt % composition:
Nineteen (19) samples were analyzed from the Raha Formation for their Sand-Clay-
Silt % composition. The fraction finer than 0.063 mm in the sediments of the Raha Formation
is dominated by the mud and clay composition forming 24.0 % and 16.0 % respectively. The
sandy mud and sandy clay samples, each constitute 21.0 % of the examined sediments,
mainly present at G. Nezzazat. Silts and sandy silts constitute about 42.0 % of the argillaceous
fraction of the Raha Formation.
c- The vertical variation diagram in the lithologic constituent:
The vertical variation diagram of carbonate-sand –mud % composition and sand-claysilt
% composition of Raha Formation indicate that Abu Had Member in the study area is
generally more calcareous than Mellaha Sand Member. Moreover, the sand content is very
rare at G. Nezzazat, whereas it is markedly rich in G. Ekma and display upward decrease
toward the base of Mellaha Sand Member. A sudden sand-enrichment is obviously recorded
at the Mellaha Sand Member allover the study area. The mud content almost shows regular
variation through the Raha Formation in the study area with slight increase toward the top of
Abu Had Member (G. Nezzazat) and its middle parts (G. Ekma). Generally, the mud
composition is more clayey than silty with almost regular vertical variation through Abu Had
Member of G. Nezzazat whereas they are more silty in G. Ekma.
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1.2.2. Abu Qada Formation:
a- Carbonate-Sand-Mud % composition:
Forty-four (44) samples represent Abu Qada Formation were analyzed for their
carbonate-sand-mud % composition. Generally, Abu Qada Formation shows a variable
composition indicating different detrital sources and variable depositional regimes. However,
the composition is more muddy in the western parts. The formation is generally dominated
with calcareous mud and muddy limestone composition, forming about 31.0 % and 25.0 % of
the formation sediments respectively. Calcareous muddy sands and calcareous sandy mud
constitute 16.0 % and 9.0 % respectively, whereas mud facies are less common, forming
about 1.0 % of the formation.
b- Sand-Clay-Silt % composition:
Thirteen (13) samples were analyzed from Abu Qada Formation for their Sand-Clay-
Silt % composition. The argillaceous fraction of Abu Qada Formation is generally dominated
with clay and mud composition, each constitutes about 38.0% of the samples. Sandy clays
constitute about 16.0 % of the formation whereas silts and silty sands are uncommon and each
constitutes about 8 % of the formation sediments.
c- The vertical variation diagram in the lithologic constituent:
The vertical variation diagram of carbonate-sand-mud % composition and sand-claysilt
% composition of Abu Qada Formation show that the formation is generally rich in
carbonate and mud compositions. However, a few amounts of sands are encountered at the
middle parts of the Upper Cenomanian of G. Nezzazat as well as, the lower Turonian part of
G. Ekma. The argillaceous facies are generally more clayey rather than silty with no specific
vertical variations.
1.2.3. Wata Formation:
a- Carbonate-Sand-Mud % composition:
Forty (40) samples represent the Wata Formation were analyzed for their carbonatesand-
mud% composition. The sediments of Wata Formation are generally composed of
almost equal proportions of lime and mud. The limestones only constitute 10.0 % of the
formation sediments. Muddy limestones and calcareous mud, on the other hand, form the
main constituent of the present sediments, forming about 40 % and 30 % respectively.
Mudstones are less abundant, forming about 10.0 % and similarly calcareous sandy mud (5.0
%) and calcareous muddy sands (5.0 %) constitute minor proportions in the present
lithological composition.
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b- Sand-Clay-Silt % composition:
Eleven (11) samples were analyzed from Wata Formation for sand-clay-silt %
composition. The argillaceous constituents of the Wata Formation generally have clay
composition, forming about 73 % of the argillaceous sediments. The Mud and sandy mud
argillaceous fraction constitutes about 17 %.
c- The vertical variation diagram in the lithologic constituent:
The vertical variation diagram of carbonate-sand –mud % composition and sand-clay silt
% composition of Wata Formation indicate that the succession of Wata Formation is
markedly rich in mud composition at the lower parts, mainly composed of high content of
clay fraction and minor amount of silt. The carbonates, on the other hand display general
upward increase in the successions examined in the study area.
1.2.4. Matulla Formation:
a- Carbonate-Sand-Mud % composition:
Seventy-three (73) samples represent the Matulla Formation were analyzed for their
carbonate-sand-mud % composition. The sediments of the Matulla Formation show wide
scattered distribution in their forming constituents reflecting obvious variation in their
sources and variability in the depositional regime. Thus, the sediments vary in composition
between mudstones, sandstones and limestones. However, the calcareous mud constitutes the
main composition, forming about 28.0 % of the formation sediments. The other calcareous
sediments are not uncommon of the calcareous sandy mud, form about 20.0 %, muddy
limestones form about 26 % and the calcareous muddy sands constitute about 9.0 %. The
different types of sands and mud constitute minor proportions.
b- Sand-Clay-Silt % composition:
Thirteen (13) samples were analyzed from Matulla Formation for their sand-clay-silt
% composition. The argillaceous fraction of the Matulla Formation is generally poor in silt
fraction (only 8.0 %). They commonly fall in the category of clayey to muddy composition.
Clays and sandy clays constitute 46 % of the sediments, whereas mud and sandy mud form
about 46 %.
c-The vertical variation diagram in the lithologic constituent:
The vertical variation diagrams of carbonate-sand-mud % composition and sand-claysilt
% composition of Matulla Formation shows that the succession of Matulla Formation is a
siliciclastic rich succession, markedly rich in sand rich-sediments at lower and middle parts
with subordinate amounts of mud and carbonates. The upper parts are usually rich in mud and
carbonates. The carbonates display general upward increase in the succession of the Matulla
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Formation in the study area, although at G. Ekma these top levels are characterized by the
presence of more sand contents. The mud-rich samples are generally clayey rather than silty
with no specific vertical variation along the succession of the present formation.
1.2.5. Sudr Chalk:
a- Carbonate-Sand-Mud % composition:
Nine (9) samples represent the Sudr Chalk at G. Nezzazat (were analyzed for their
carbonate-sand-mud% composition. The analyzed samples are totally composed of limestones
composition.
b- The vertical variation diagram in the lithologic constituent:
The vertical variation diagram of carbonate-sand –mud % composition of Sudr Chalk
indicates that the succession of Sudr Chalk is a generally monotonous succession, consisting
of a homogeneous calcareous composition.
1.3. Microfacies Analysis and Depositional Trends:
The recognized microfacies associations in each rock unit are discussed as follows:-
1.3.1. The Raha Formation:
Eight microlithofacies were recognized in this rock unit. The microfacies trends of the
Raha Formation proved deposition under gradual marine deepening conditions related to a
gradual sea-level rise of a subtle advancing sea started with the Cenomanian. The deposition
started within the realm of shallow supratidal and intertidal subenvironments. The deepest
marine setting in this episode lies with the depth of intertidal to shelf lagoons. The continuous
Cenomanian sea-level rise resulted in the evolution of deeper subenvironments of shelf bays
and reached the maximum sea-level rise during inner-shelf environment. Toward the top of
Raha Formation, a marked sea-level DROP and land-ward shift of the sea-shore occurred
marked by the deposition of supratidal environment.
1.3.2. Abu Qada Formation:
Seven microlithofacies were recognized in this rock unit. With the Deposition of this
formation, the shallow supratidal, intertidal and shelf lagoonal marine settings encountered
below (top of Raha Formation) continued during the early stages of this formation. However,
these shallow marine facies gave-way to facies of deeper marine (shelf bays to inner-shelf
marine settings). Minor shallow marine fluctuations during the generally advancing sea-level
rise are present as evidenced by intertidal sandstones were intervening the deeper facies.
1.3.3. Wata Formation:
Four microlithofacies were recognized in this rock unit. The formation represents a
depositional episode of relatively deep marine environments related to a remarkable sea-level
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rise. The deposition was within deep marine mid/outer shelf conditions related to high sealevel
settings. These conditions continued to dominate the entire depositional phase of Wata
Formation.
1.3.4. Matulla Formation:
Fourteen microlithofacies were recognized in this rock unit. The Matulla Formation
represents a phase of unstable sea-level conditions where, marked sea-level fluctuations were
dominating the entire depositional time of the formation in the study area. The deposition of
Matulla Formation started during a phase of sea-level DROP associated with noticeable landuplifts
resulted in the dominance of shallow intertidal and shelf lagoonal facies. Toward the
middle parts of the formation, a marked sea-level rise took place accompanied with relatively
deep marine sedimentation, where shelf bays and middle to outer marine shelf facies were
deposited. These relatively deep marine conditions were occasionally intervened with shortlived
shallow intertidal episodes. These deep marine conditions came to close toward the end
of the upper parts of the formation, where a marked sea-level DROP took place accompanied
with shallow intertidal and supratidal warm coastal sedimentation
1.3.5. Sudr Chalk:
One dominant microlithofacies was recognized in this rock unit. Sudr Chalk in the
study area represents a phase of relatively deep marine conditions. The examined microfacies
display a monotonous facies type related to middle-outer shelf marine conditions.
1.4. Sequence Stratigraphic Analyses;
The detailed field studies and paleo-environmental investigations have enabled
subdivision of the Upper Cretaceous sediments into four third-order depositional sequences
and one second-order (?) depositional sequence, each represents a separate depositional event,
related to an independent marine cycle.
I- THIRD-order DEPOSITIONAL SEQUNCES:
Third-order depositional sequences are normally developed due to either tectonic
episodic local/regional events or due to local eustasy in sea-level changes (Vail et al., 1977 &
1991). They have local or global distribution with depositional duration of 0.5-3.0 m.y.
(Mitchum and Van Wagoner, 1991; Posamentier et al., 1991).
1.4.1. The Depositional Sequence (SQ-1):-
1.4.1.1. Distribution:-
SQ-1 is the lowermost depositional sequence in the Upper Cretaceous succession in
the study area. It encompasses the entire sediments of the Cenomanian Raha Formation. The
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sequence overlies the Early Cretaceous Malha Formation, while underlies the depositional
sequence ”SQ-2”. The SQ-1 generally consists of a mixed siliciclastic/carbonate units and
display almost uniform thickness ranging between (63.0) m in the south, and (55.0) m in the
north. The age of this sequence is generally Early-Middle Cenomanian due to the presence
below the Late Cenomanian-Early Turonian Abu Qada Formation.
1.4.1.2. The Sequence Boundaries
The field studies prove that the lower sequence boundary (Sb-1) of the present
sequence displays a marked erosional irregular contact with the underlying Early Cretaceous
Malha Formation and considered type-1 sequence boundary. The upper sequence boundary
(Sb-2), on the other hand, is a conformable transitional surface marked by the passage from
the warm supratidal shallow marine conditions of SQ-1 below, into relatively deeper shelf bay
marine environments of SQ-2 above and considered as of type-2 sequence boundaries.
1.4.1.3. The Transgressive Surface (ts-1):
The transgressive surface (ts-1), of SQ-1 is recorded all-over the study area. It is
delineated here on the basis of the marked depositional facies changes and parasequences
architecture. Along ts-1 in the study area a remarkable facies change from short-lived
supratidal/intertidal depositional environments into deeper open shelf to inner shelf marine
conditions.
1.4.1.4. The maximum flooding surface (mfs-1):
The mfs-1 of SQ-1 is recorded all-over the study area. It is delineated when the deep innermiddle
marine shelf facies were successively prograded by relatively shallower intertidal and
supratidal facies.
1.4.1.5. Systems Tracts
1.4.1.5.1. Low-stand Systems Tract (LST-1)
LST-1 is relatively thin unit, varies in thickness from 16.0 m in the south to about 13.0
m in the north. It is generally siliciclastic unit; while it consists of sandstones in the south, it is
more rich in shales with minor thin calcareous intervals in the north. The tract consists of
relatively thin retrograditional parasequences that successively onlap the underlying Malha
Formation through Sb-1.
1.4.1.5.2. Transgressive Systems Tract (TST-1)
TST-1 ranges in thickness from 21.0 m in the south to 28.0 m in the north. It is
generally consisting of a mixed siliciclastic/carbonate unit with rather enrichment in
limestones toward the upper parts. The tract is composed of relatively thick
retrograditional/aggradational parasequences with laterally extensive, weakly undulating
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transitional contacts. Due to the continuous sea-level rise, the accommodation volume was
gradually increased and become greater than that of sediment-supply (A>S), thus relatively
thick deeper inner-middle marine shelf parasequences were developed.
1.4.1.5.3. Highstand Systems Tract (HST-1)
HST-1is delineated all over the study area. It ranges in thickness from 19.0 m in the
south to 15.0 m in the north. Lithologically, the tract consists of a mixed shale/limestone unit,
especially at the upper half. It is composed of relatively thin prograding parasequences with
flat planar contacts. The rapid basin land-ward shift accelerated the rate of deposition than
that of the accommodation volume (S>A). Thus, shallow intertidal quartz arenites were
prograded upward by supratidal gypsiferous facies. Numerous intervals of thin fissile
gypsiferous shales with ferruginous bands are reported at the top parts of this tract marking
the maximum sea-level DROP during SQ-1, just prior to Sb-2.
1.4.2. The Depositional Sequence (SQ-2):-
1.4.2.1. Distribution:-
SQ-2 is recorded in the examined successions following upward SQ-1. It encompasses
the sedimentary succession of Abu Qada Formation, Wata Formation and the lowermost 10-
15 m of Matulla Formation. The age of this sequence ranges between Late Cenomanian to
earliest Coniacian. It is relatively the thickest sequence in the examined successions. It ranges
in thickness from 89.0 m in the south to 101.0 m in the north. This thick sequence consists of
general siliciclastic/carbonate intercalations with noticeable enrichment of carbonate
limestones in the middle parts.
1.4.2.2. The Sequence Boundaries
The SQ-2 overlies the Sb-2 mentioned above (6.1.2) having the characters of type-2
boundaries, and is recorded in the examined successions. The upper sequence boundary Sb-3
marks the maximum sea-level DROP at the end of SQ-2, associated with the dominance of
supratidal and intertidal depositional episode. This proves no coastal emergence due the
landward shift of the coast-line during the time of Sb-3. The volume of the accommodation
zone reached minimum at the time of the given boundary, enabling the prevalence of only
foreshore intertidal sub-environments. In this study, Sb-3 is arbitrary placed within these very
shallow facies and starting the evolution of the overlying SQ-3.The stratigraphic and
depositional characteristics of the Sb-3 generally prove that it is of Type-2 sequence
boundary.
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1.4.2.3. The Transgressive Surface (ts-2):
The transgressive surface (ts-2) is recorded in the examined successions with almost
the same characters. It marks the actual advance of the sea-level when the middle - outer shelf
facies overlap the shallower intertidal ones below, indicating the start of proper increase in the
volume of the accommodation zone. Intervals very rich in Ammonite Choffaticeras
(Leoniceras) segne (Solger) indicate the early signs of the advent of ts-2 in the study area.
The ts-2 is herein placed along the time of a dominant sea-level rise, most likely with the
lower boundary of the Wata Formation (middle to late Turonian).
1.4.2.4. The maximum flooding surface (mfs-2):
The maximum flooding surface (mfs-2) is delineated throughout the study area
marking the maximum sea-level rise. It represents the widest volume of the accommodation
zone ever recorded during SQ-2. It is marked when the final sea retrogradation over the study
area took-place. The exact position of the mfs-2 is placed when the above mentioned deeper
facies are markedly prograded with very shallow intertidal flat and lagoonal facies, indicating
the start of a phase of sea-level DROP due to sea gradual progradation accompanied with a
reduction of the accommodation zone.
1.4.2.5. Systems Tracts
1.4.2.5.1. Shelf Margin Systems Tract (SMST-2)
Shelf Margin Systems Tract (SMST-2) was recorded at the early depositional stages of
SQ2 all over the study area. It overlies sequence boundary Sb-2 having the character of type-
2. The tract is recorded ranging in thickness from 40.0 m in the south to 62.0 m in the north. It
is generally consists of a mixed siliciclastic-carbonate unit, however, the limestones display
some enrichment toward the upper parts of the tract. The present SMST-2 is composed of
successive parasequences having transitional undulating contacts. The parasequences were
initially developed having an aggradational architecture that were developed within
dominantly shelf-bay and inner-shelf marine sub-environments. These parasequences were
successively overlapping Sb-2, expressing very gradual sea-level rise and subtle increase in
the accommodation zone. Upwards, with the continuous sea-level rise coupled with the
increase of the depositional zone, the parasequences acquired retrograditional attitude
deposited within relatively deep marine conditions. They include inner to middle shelf
settings, representing a general transgressive phase toward the transgressive surface ts-2.
1.4.2.5.2. Transgressive Systems Tract (TST-2)
Transgressive Systems Tract (TST-2) is delineated along the study area achieving the
deepest marine conditions ever recorded in the study area. The tract varies in thickness from
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51.0 m in the north to 30.0 m in the south. It is generally thick carbonate unit with minor
siliciclastic intercalations especially in the southern parts of the study area. The tract is built
of thick parasequences generally exhibiting transitional planar contacts. The parasequences
commence with initial retrograditional architecture. These parasequences are essentially
consisting of different facies abundantly deposited within inner-middle shelf marine settings
with minor foreshore intercalations. Upwards, the parasequences prove relatively gradual
thickening indicating continuous deepening of the accommodation zone as the sea-level
continuously rise (A>S).
1.4.2.5.3. Highstand Systems Tract (HST-2)
Highstand Systems Tract (HST-2) is the topmost tract in SQ-2, and it is as reported
all-over the study area (Figs 6.1 and 6.2). HST-2 is generally siliciclastic/carbonate unit
ranging in thickness from 19.0 m in the south to 12.0 m in the north. It consumes the rock
stratigraphic unit of the top 8.0 m of the Wata Formation and the lower 20.0 m of the Matulla
Formation. With deposition of HST-2, the sea-level recorded short-lived still-stand characters
of relatively deep middle/outer shelf marine conditions. These resulted in relatively thin
aggradational parasequences of Dolomitized wackestone and Peloidal grainstone facies,
displaying erosive basis. However, the progressive evolution of HST-2 was influenced by
successive sea-level fall and reduction of the accommodation volume (S>A).
1.4.3. The Depositional Sequence (SQ-3):-
1.4.3.1. Distribution:-
This sequence is recorded all-over the study area and follows the succession of SQ-2
without depositional break, however a marked sea-level fall is traced in between during Sb-3.
In the northern parts (G. Nezzazat), this sequence encompasses the sedimentary unit
succeeding Sb-3 of the Matulla Formation, measuring ~ 102.0 m and in the southern parts (G.
Ekma), this sequence includes the entire upper part of the Matulla Formation (60.0 m)
cropping-out between Sb-3 and the overlying Sudr Chalk (Campanian-Maastrichtian). Mostlikely,
the age of this sequence falls within Late- Coniacian/Santonian interval of the Matulla
Formation (Coniacian-Santonian). SQ3 is generally consisting of non-rhythmic alternation
between siliciclastic and carbonate units. The observed thickness variation in SQ-3 from the
south to north is attributed to an active erosive phase succeeding the land-uplifts took-place
with the end of Santonian and resulted in the angular unconformable relation recorded with
the Sudr Chalk.
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1.4.3.2. The Sequence Boundaries
The SQ-3 overlies the Sb-3 having the characters of type-2 boundaries and the upper
sequence boundary Sb-4 is only recorded in the northern parts (G. Nezzazat). It is absent in
the southern parts (G. Ekma), and instead, the present SQ-3 is topped against the angular
unconformity contact (Sb-5) with Sudr Chalk.
Sb-4 marks a stage of remarkable sea-level DROP and coastal emergence accompanied
with sub-aerial activities. It seems that the study area, during the time span of Sb-4, had
undergone a long time interval of very shallow intertidal and evaporitic warm supratidal
coastal deposition. Thin ferruginous duricrusts were many recorded at the top-parts of this
interval. Moreover, distal alluvial channels were evolved and shaped the landscape around the
northern parts of the study area at the time of Sb-4. These alluvial channels managed to
incise-into the coastal flats that emerged at that time, depositing feldspar-rich sandstones with
many wood remains (Feldspathic quartz arenite) as terrestrial loads within these emerged
coastal-flats, ending the depositional history of SQ-3. Based upon the stratigraphical
geometry and depositional characteristics along the time of Sb-4 mentioned above, it is
proved that Sb-4 is of type-1 sequence boundary.
1.4.3.3. The maximum flooding surface (mfs-3):
The maximum flooding surface (smf-3) is a common surface, always recorded along
the entire area. It is delineated when the sea-level reached maximum, associated with the
ultimate volume of the accommodation ever occurred during SQ-3. This situation is herein
recorded when aggradational outer shelf marine facies including Wackestone and
Foraminiferal packstone started to be prograded upward by shallower intertidal and supratidal
facies.
1.4.3.4. Systems Tracts
1.4.3.4.1. Transgressive Systems Tracts (TST-3):
As SQ-3 onlaps directly the type-2 sequence boundary (Sb-3), it was expected that the
deposition would started with shelf-margin systems tracts as recorded below (SQ-2).
However, detailed inspection of both architecture and depositional characters of the
parasequences forming TST-3 assume rapid basin-submergence coupled with remarkably
accelerating sea-level rise, and increasing volume of the accommodation zone (A>>S). This
situation commonly becomes available when a sudden marine transgressive event dominates
the area of deposition producing actual transgressive systems tract. Thus, the sedimentary unit
under consideration is herein regarded as transgressive system tract first overlapping Sb-3
during the deposition of SQ-3.
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1.4.3.4.2. Highstand Systems Tracts (HST-3):
HST-3 is recorded in the study area varying in thickness from 38.0 m in the south to
35.0 m in the north. It consists of actively retrograding parasequences rapidly evolved from
shallow intertidal to deep outer shelf marine subenvironments, expressing rapid increase of
the accommodation volume (A>S). Toward the close of this tract, the sea-level reached
maximum, and the ultimate volume of depositional medium was arrived just with the mfs-3.
Transgressive Systems Tracts (TST-3) is recorded along the study area. It is generally
calcareous/siliciclastic unit ranging in thickness 22.0 m in the south to 61.0 m in the north. By
the close of TST-3, a strong sea-level DROP took place in an accelerating rate with intense
basin landward-shift, especially in the northern parts. Accordingly, the volume of the
accommodation zone was successively reduced against a relatively increasing sedimentation
rate (S>A). Therefore, the outer shelf marine facies seen at the top of TST-3 were prograded
by prograditional parasequences of shallow intertidal and evaporate-rich supratidal facies.
These very shallow marine conditions lasted for a considerable time consuming the entire
HST-3 especially in the northern parts.
Toward the end of the HST-3, the area was dominated with intertidal and supratidal
evaporitic coastal conditions, coupled with subaerial emergence and duricrusts formation as
well as incising channels as recorded along the Sb-4. In the southern parts the history of HST-
3 and SQ-3 was closed toward the unconformable sequence boundary Sb-5.
1.4.4. The Depositional Sequence (SQ-4):-
1.4.4.1. Distribution:-
SQ-4 is only recorded in the northern parts of the study area (G. Nezzazat). The
sequence overlies SQ-3 through Sb-4 (type-2) boundary. It measures a thickness of 31.0 m.
the sequence is generally carbonate unit with minor siliciclastic interval at the top below the
erosional contact Sb-5. The SQ-4 terminates the Santonian history in the study area.
1.4.4.2. The Sequence Boundaries
SQ-4 rests directly over Sb-4 having the characters of type-1 sequence boundary and
the upper sequence boundary (Sb-5) is an unconformable surface contact with low-angular
relation with the overlying Sb-5 of Sudr Chalk (Campanian-Maastrichtian).
1.4.4.3. Systems Tracts
SQ-4 is, in fact, incomplete third order depositional sequence. Much of this sequence
was eroded due to the uplift tectonic disturbances took place at the end of Santonian. The
sequence is only represented in the study area by a lowstand-wedge of LST-4.
14
This tract consists of retrograditional parasequences of relatively deeper marine
conditions developed in the realm of inner-outer shelf conditions. These parasequences
strongly onalpped the supratidal sedimentation and subaerial emergence prevailed during Sb-
4 (type-1). These depositional characters indicate that the SQ-4 started with a significant
basin-ward shift associated with gradual increase of the accommodation volume.
I- SECOND-order (?) DEPOSITIONAL SEQUNCES:
The second-order depositional sequences are commonly developed due to either
tectonic non-episodic regional events (tectonic subsidence and sediment-supply) or due to
global eustasy in ocean-basin volume (Vail et al., 1977 & 1991). They have local or global
distribution with depositional duration of 50 – 3.0 m.y. (Mitchum and Van Wagoner, 1991;
Posamentier et al., 1991).
1.4.5. The Depositional Sequence (SQ-5):-
The SQ-5 is the topmost depositional sequence in the Upper Cretaceous succession of
the study area. The sequence is entirely encompasses the succession of the Sudr Chalk. It
ranges in thickness from 28.0 m in the south to 90.0 m in the north. The observed thickness
variation encountered in the study area is attributed to the tectonic disturbances associated
with differential land-uplifts together with a substantial sediment-removal took place during
Upper Cretaceous/Lower Tertiary times. The sequence consists of an almost monotonous
lithologic composition of snow-white fossiliferous chalk.
SQ-5 is bounded on both lower (Sb-5) and upper (Sb-6) surfaces by unconformity
surfaces related to regional tectonic events recorded throughout Sinai (Moustafa & Khalil,
1990; Issawi et al. 1999; Khalil, 1999; Bauer et al. 2003). They are, thus of type-1 sequence
boundaries of Van Wagoner et al (1988).The available data concerning this sequence indicate
that the sequence encompasses thick aggradational parasequences of foraminiferal biomicrites
with transitional undulating contacts, related to deep transgressive marine conditions,
commonly associate remarkable sea-level rise and considerable increase of accommodation
zone. Most-likely, the tectonic deformation predated the evolution of the SQ-5 resulted in
considerable increments in the accommodation zones within which the sequence was
deposited.